Auto-focusing system

ABSTRACT

An auto-focusing system includes a focus condition detector which detects the focus condition based on infrared light. A data producer is provided for producing a deflection signal indicating the difference between an image forming distance for infrared light and that for visible light, due to aberration. In accordance with the detected focus condition and deflection signal, an objective lens is shifted to a position for properly focusing an image of visible light on an image forming plane.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an auto-focusing device and method of acamera of an interchangeable objective lens type and, more particularly,to an auto-focusing system wherein the reflected light from an object tobe photographed passes through the objective lens of the interchangeablelens and forms an image on or near a predetermined image forming plane,which image is detected for detecting the degree of out of focus,thereby controlling the lens shift by the detected degree of out offocus. The present invention also relates to an interchangeable lensitself for use in the above described type of camera.

2. Description of the Prior Art

There have been conventionally proposed various types of the abovedescribed auto-focusing method, but most of them use visible light.Therefore, when the intensity of the visible light is very weak, such aswhen the scenery is dark, it is very difficult to detect the focusingcondition of the target object, resulting in an error control of theobjective lens. Also, for detecting the image, a charge accumulatingdevice, such as CCD, can be employed, but would result in a disadvantagethat the charging period becomes long as the visible light becomes weak,resulting in long time of focus detection.

It is known in the art that the photoelectric conversion device, such asCCD or photodiode, for use in focus detection is generally moresensitive to infrared rays than the visible rays. Also, it is known inthe art that the infrared rays reflect at a high rate even on a blackobject and also on an organic object.

From this view point, it is possible to detect, if the infrared ray areused for focus detection, the focusing condition of an object even ifthe object is located in a dark place, and consequently improving thefocus detection ability.

But, on the other hand, if the infrared rays are used for focusdetection, it takes a disadvantage that there will be a difference infocusing distance between the the infrared rays and the visible rays,due to color aberration, and such a difference varies as the type of aninterchangeable lens mounted on a camera body changes. Therefore, unlessa suitable correction is effected, a picture taken by an auto-focusingsystem using the infrared rays always results more or less in out offocus.

To remove the above disadvantage, an improved auto-focusing system isproposed in Japanese Patent Laid-open Publication (Tokkaisho) No.57-154224, wherein a signal pin having a length corresponding to thefocusing distance difference is provided to each interchangeable lens,and a focus detecting device having a means to correct the focusingdistance difference by the signal pin are provided. According to theproposed device as described above, the signal pin extending from thelens must have a required strength to avoid undesirable break or bent,and also the signal pin should be positioned with a high accuracy toenable the precise correction. Also, the focus detecting device providedin the camera body will have a complicated structure, resulting in highmanufacturing cost, and because of the complicated structure, it may notbe able to correct the difference to the required degree due to theinaccuracy of size and positioning of each constructing part.

Furthermore, according to the auto-focusing device disclosed inTokkaisho No. 57-154224, it is very difficult to detect the focusingwhen a target object is under a weak visible light and yet containingalmost no infrared rays, such as under fluorescent lamp, not only whendetecting the focus condition by way of vible light, but also by way ofinfrared rays. Moreover, if the target object has no or hardly anycontrast, such as in the case of plain wall, it is very difficult todetect the focus condition even when using the infrared rays.

Another improved auto-focusing system is proposed in Japanese PatentLaid-open Publication (Tokkaisho) No. 57-150808, which is so designedthat the focus condition can be detected either by the visible rays orinfrared rays. The auto-focusing system according to Tokkaisho No.57-150808 comprises two photoelectric conversion means, one for visiblerays and the other for infrared rays, and a beam splitter for dividingthe rays from the object in terms of amount into rays to be directed tothe visible light photoelectric conversion means and to the infraredlight photoelectric conversion means. An infrared cut filter is disposedbetween the visible light photoelectric conversion means and beamsplitter for cutting the infrared rays to be directed to the visiblelight photoelectric conversion means. Each photoelectric conversionmeans is connected, through a discrimination circuit, to a selectioncircuit and further to a focus condition detecting circuit.

According to the auto-focusing system of Tokkaisho No. 57-150808, it isstated that when no infrared light pass filter is used to carry outphotographing using visible rays, almost the same amount of lightimpinges on both photoelectric conversion means and, therefore, theoutputs from both photoelectric conversion means have approximately thesame level. Thus, the discrmination circuit discriminates that the ratioof outputs from both photoelectric conversion means is approximatelyequal to one, thereby actuating the selection circuit to select outputfrom the visible light photoelectric conversion means.

It further states that when the infrared light pass filter is used tocarry out photographing using infrared rays, the amount of lightimpinging on the infrared light photoelectric conversion means isgreater than that on the visible light photoelectric conversion means.Thus, the discrimination circuit discriminates that the ratio of outputsfrom both photoelectric conversion means is not equal to one, therebyactuating the selection circuit to select output from the infrared lightphotoelectric conversion means.

The focus condition detecting circuit operates in response to the outputsignal selected by the selection circuit.

From a practical point of view, however, there are a variety of objectsdiffering from one another in reflection properties. Thus, it is notalways true that the ratio between outputs from the visible lightphotoelectric conversion means and from the infrared light photoelectricconversion means is constant with use of no infrared light pass filter.Thus, it is practically very difficult to set a level or borderline forcausing selection of an output from visible light photoelectricconversion means whenever photographs are taken using the visible light.Therefore, even when the output from the visible light photoelectricconversion means is selected, there may be a case wherein the focusdetection is carried out using the infrared rays, resulting in out offocus, because there is a difference in an image forming distance of theobjective lens between the visible rays and infrared rays. Moreover,when taking a photograph under the A-light source (tungsten type lamp)or under the natural light, there may be a case in which the infraredrays are stronger than the visible rays. In such a case, thephotographing is carried out using the visible rays, but the focusdetection is carried out using infrared rays, resulting in an error infocus adjustment.

Also, according to the prior art, it is well know to emit an auxiliarylight to the object, when the object is too dark to carry out the focusdetection. In this case, if the object is people, and when the auxiliarylight is visible light, such an auxiliary light makes people unpleasant.In order to overcome this, an improved focus detecting device isdisclosed in Japanese Patent Laid-open Publication (Tokkaisho)55-111929, which device emits, instead of visible lights, infrared raysas the auxiliary light when the target object is very dark and has lesscontrast. However, Japanese Patent Laid-open Publication (Tokkaisho)55-111929 does not take any consideration to the difference in focusingdistance between the the infrared rays and the visible rays, due tocolor aberration of the objective lens.

SUMMARY OF THE INVENTION

The present invention has been developed with a view to substantiallysolving the above described disadvantages and has for its essentialobject to provide an improved auto-focusing system which can carry outan auto-focusing operation for the visible light using infrared rayswith high accuracy, without employing any mechanical or opticalcorrecting means.

It is also an essential object of the present invention to provide anauto-focusing system of the above described type which can carry out anauto-focusing operation quickly and accurately, with an aid of emissionof infrared rays, even when the target object is dark or has a lowcontrast.

It is a further object of the present invention to provide aninterchangeable lens suited for use with a camera eploying anauto-focusing system of the above described type.

According to the auto-focusing system of the present invention, a focuscondition is detected based on the infrared light. A data producer isprovided for producing a deflection signal indicating a differencebetween an image forming distance for the infrared light and that forthe visible light, due to aberration. In accordance with the detectedfocus condition and deflection signal, an objective lens is shifted to aposition for properly focusing an image of visible light on apredetermined image forming plane.

Furthermore, according to the present invention, an auxiliary lightsource for emitting infrared light is provided for lighting an object,thus facilitating the focus cndition detection. According to oneembodiment, a dark object is brightened by the emitted infrared light toincrease the detecting level, and according to another embodiment, aplain object, such as a wall, is spot-lighted by the emitted infraredlight to provide a contrast.

Moreover, according to the present invention, the objective lens can beshifted in one step or in two steps to bring it to the properly focusedposition for the visible light. In the case of one step, an amount oflens shift is calculated using the detected focus condition based on theinfrared light and deflection signal, and then, the lens is shifted inaccordance with the calculated result. In the case of two steps, thelens is first shifted based on the focus detection under theinfraredlight, and is shifted again based on the deflection signal.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and features of the present invention willbecome apparent from the following description taken in conjunction withpreferred embodiments thereof with reference to the accompanyingdrawings, throughout which like parts are designated by like referencenumerals, and in which:

FIG. 1a is a block diagram of an auto-focusing system according to thepresent invention;

FIG. 1b is a diagrammatic view showing an optical arrangement of theauto-focusing system of the present invention employed in a camera;

FIG. 2a is a graph showing a spectral sensitivity of a visible lightphotoelectric conversion means and a normalized reflectance of a firstreflecting face of a beam splitter;

FIG. 2b is a graph similar to FIG. 2a, but particularly showing aspectral sensitivity of an infrared light photoelectric conversionmeans;

FIG. 3 is a diagrammatic view showing one example of a beam splitteremployed in the auto-focusing system of Fig. 1a;

FIG. 4 is a graph showing a normalized reflectance of a junction face ofglass blocks of defining the beam splitter of FIG. 3;

FIG. 5 is a diagrammatic view showing another example of a beamsplitter;

FIG. 6 is a graph showing a normalized reflectance of the beam splitterof FIG. 5, particularly when the incident angle of beam is 45° ;

FIG. 7 is a diagrammatic view showing a major portion of opticalarrangement employing the beam splitter of FIG. 5;

FIGS. 8a and 8b taken together show a circuit diagram of anauto-focusing system according to one embodiment the present invention,wherein characters A-E in FIG. 8a are connected to correspondingcharacters in FIG. 8b;

FIG. 9a and 9b taken together show a detailed circuit diagram or circuitand data output circuit shown in FIG. 8b, wherein characters J1-J4 inFIG. 9a are terminals connectable to terminals in FIG. 9b withcorresponding characters;

FIGS. 10 and 11 are circuit diagrams showing modifications of thecircuit shown in FIG. 9b;

FIGS. 12a and 12b taken together show a flow chart of the auto-focusdetection carried out by the circuit of FIGS. 8a and 8b, whereincharacters F-I in FIG. 12a are connected to corresponding characters inFIG. 12b;

FIG. 13 is a circuit diagram showing a major portion of an auto-focusingsystem according to another embodiment the present invention;

FIG. 14 is a circuit diagram showing a major portion of an auto-focusingsystem according to yet another embodiment the present invention;

FIG. 15 is a flow chart of the auto-focus detection carried out by thecircuit of FIG. 14;

FIG. 16 is a flow chart similar to FIG. 15, but showing only a modifiedportion;

FIG. 17 is a flow chart showing a detail of a step #51 of FIG. 15 or 16for the detection of contrast;

FIG. 18 is a diagrammatic view of a camera installed with a device foremitting infrared rays to an object to be photographed;

FIG. 19 is a diagrammatic view of an interchangeable lens installed witha device for emitting infrared rays to an object to be photographed;

FIG. 20 is a diagrammatic exploded view of a filter employed in theinterchangeable lens of FIG. 19, particularly showing an arrangement foremitting infrared rays; and

FIG. 21 is a circuit diagram of an auto-focusing system according to afurther embodiment the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1a, a block diagram of an auto-focusing system of thepresent invention is shown. A reference number 2 designates an objectivelens included in an interchangeable lens; 7 designates a beam splitterdefining a major portion of an optical arrangement of focus detector;and 9a and 9b designate photoelectric conversion devices for visiblelight and infrared light, respectively. The beam splitter 7 is providedfor splitting the light from a target object and passed through the lens2 into visible light and infrared light, and for this purpose, it has afirst and second reflecting faces 7a and 7b. The first reflecting face7a has a normalized reflectance (normalized in percentage of reflectedlight when the incident light is rendered as "1") as shown by a realline in FIG. 2a, and a normalized transmittance (normalized inpercentage of transmitted light when the incident light is rendered as"1") as shown by a real line in FIG. 2b. As apparent from the graphs ofFIGS. 2a and 2b, lights having wavelength of about 700 nanometers orlonger, i.e., lights in infrared and/or near-infrared region, arereflected on the first reflecting face 7a, and lights having wavelengthof less than about 700 nanometers, i.e., visible lights, are transmittedthrough the first reflecting face 7a.

A term infrared used herein includes a range in which photoelectricconversion device 9b for the infrared light is sensitive, such as lightshaving wavelength of 650-900 nanometers. Thus, a term infrared usedherein includes near-infrared and partly visible lights of longwavelength.

The photoelectric conversion device 9a is so located as to receive thelights transmitted through the first reflecting face 7a. Thus it mainlyreceives visible lights. The photoelectric conversion device 9b is solocated as to receive the lights reflected from the second reflectingface 7b which has a high reflectance at least in the infrared region.Thus, the photoelectric conversion device 9b mainly receives infraredlights.

Instead of the beam splitter 7 described above, a normal beam splitterwhich merely splits the lights in terms of amount can be employed. Inthis case, a filter for cutting infrared rays should be provided infront of the visible light photoelectric conversion device 9a, and afilter of cutting visible light should be provided in front of theinfrared light photoelectric conversion device 9b.

Referring to FIG. 1b, an optical arrangement of a single-reflexinterchangeable lens type camera employing the auto-focusing system ofthe present invention is shown. A reference number 1 designates a mainmirror defined by a half-mirror plate; 6 designates a submirrorsupported by the main mirror 1; 8a and 8b designate relay lenses; 3 is apentaprism; 4 is an eyepiece lens; 5 is a focus plate; and 10 is apredetermined image forming plane (film plane) for which objective lens2 is to be adjusted to focus visual light thereon. Both main mirror 1and submirror 6 have a uniform reflectance characteristic to all colorsincluding visible light and infrared light. The photoelectric conversiondevices 9a and 9b have a normalized spectral sensitivity (normalized inpercentage when the maximum sensitivity is rendered as "1"), as shown bya dotted line in FIGS. 2a and 2b.

Because of the color aberration of the objective lens, an image formingdistance for the infrared light is longer than that for the visiblelight by an amount dL, and such an amount dL is referred to asdeflection dL. The deflection dL varies with respect to the type ofinterchangeable lens depending on the various factors, such as numberand arrangement of lenses defining one interchangeable lens, focallength, etc. Therefore, each interchangeable lens has its own deflectiondL which is different from the deflection dL of another interchangeablelens. Furthermore, the deflection dL varies relatively to the change offocus distance, or to the change of focal length if the interchangeablelens is a zoom lens.

If the lens is shifted to an in-focus position in accordance with afocus detection carried out by the infrared lights, and thereafter, if apicture is taken with visible light, the picture will result in out offocus. To obtain a properly focused picture, in this case, it isnecessary to correct the deflection dL, which is intrinsic to each typeof interchangeable lens.

According to the optical arrangement shown in FIG. 1a or 1b, an opticaldistance between the lens 2 and relay lens 8b, or infrared lightphotoelectric conversion device 9b, is longer than an optical distancebetween the lens 2 and relay lens 8a, or visible light photoelectricconversion device 9a, by an optical distance d/n, wherein d is an actualdistance between the first and second reflecting faces 7a and 7b, and nis a refractive index of the beam splitter 7, provided that thephotoelectric conversion devices 9a and 9b are both positioned at thesame distance from the beam splitter 7. If the optical distance d/n isselected to be equal to the deflection dL for one standard lens, animage of visible light can be properly focused on the visible lightconversion device 9a as well as on predetermined image forming plane 10and, at the same time, an image of infrared light can be properlyfocused on the infrared light conversion device 9b, provided that saidone standard lens is mounted on the camera. Thus, in this case, the lenscan be properly focused for the visible light with the focus detectioncarried out by the infrared light.

If the lens is changed to another interchangeable lens having adeflection dL' which is greater than the deflection dL, such adeflection dL' can not be properly corrected by the optical distanced/n. To properly correct the deflection dL', the camera must be providedwith a following correction data S:

    S=dL'-d/n.

In the foregoing description, the infrared lights having a predeterminedwavelength should be used for determining the data S, and in the case ofusing the beam splitter 7, such a wavelength should preferably be 830nanometers, at which the production of normalized reflectance of thereflecting face 7a and normalized spectral sensitivity of thephotoelectric conversion device 9b takes the maximum value.

Referring again to FIG. 1a, both outputs from the visible lightphotoelectric conversion device 9a and from the infrared lightphotoelectric conversion device 9b are applied to a discriminationcircuit 11 and also to selection circuit 12. The discrimination circuit11 discriminates which one of the two outputs from the devices 9a and 9bis greater, and produces a discrimination signal indicating the onewhich is greater. The discrimination signal is applied to the selectioncircuit 12, and also to other circuits, such as a gate circuit 13-1provided in a focus detection calculation circuit 13. A reference number16 designates a data output circuit installed in each interchangeablelens for producing a correction data S intrinsic to each interchangeablelens. The data output circuit 16 is connectable, when the lens ismounted on the camera, to a read-out circuit 17 for supplying thecorrection data S to the gate circuit 13-1.

When the gate circuit 13-1 is receiving a discrimination signalindicating that the output from the infrared light photoelectricconversion device 9b is greater than that from the visible lightphotoelectric conversion device 9a, the gate circuit 13-1 permits topass the correction data S from the read-out circuit 17 to a subtractor13-3.

On the contrary, when the gate circuit 13-1 is receiving adiscrimination signal indicating that the output from the visible lightphotoelectric conversion device 9a is greater than that from theinfrared light photoelectric conversion device 9b, the gate circuit 13-1cuts the correction data S, and instead, provides a data representingzero to the subtractor 13-3.

The selection circuit 12 operates in such a manner that it produces theoutput from the infrared light photoelectric conversion device 9b whenthe discrimination signal indicating that the output from the infraredlight photoelectric conversion device 9b is greater than that from thevisible light photoelectric conversion device 9a. Contrary, theselection circuit 12 produces the output from the visible lightphotoelectric conversion device 9a when the discrimination signalindicating that the output from the visible light photoelectricconversion device 9a is greater than that from the infrared lightphotoelectric conversion device 9b. The output produced from theselection circuit 12 is applied to a calculation circuit 13-2 whichcalculates an amount of defocus (out of focus) of the image formed byvisual light on image forming plane 10 as well as on the device 9a, andalso a direction of defocus whether it is defocused forwardly orrearwardly. After calculating, the calculation circuit 13-2 produces adefocus signal dF representing the calculated amount and direction ofdefocus. The defocus signal dF is applied to a subtractor 13-3 whichsubtracts the data S from the defocus signal dF and produces an absolutevalue of the subtracted result, i.e., |dF-S|. When the data S is equalto zero, the subtracted result is |dF|. The subtractor 13-3 alsoproduces a signal representing + or - for the direction of defocus.

The outputs of the subtractor 13-3 are applied to a display device DPfor displaying the amount and direction of defocus as obtained from thesubtractor 13-3, and also to a lens driver LCO for driving the lens 2based on the direction of defocus signal from the subtractor 13-3.

In the foregoing description, the amount and direction of defocus can becalculated in a manner disclosed in U.S. Pat. No. 4,333,007 patentedJune 1, 1982 to Langlais et al., 4,341,953 patented July 27, 1982 toSakai et al. or in Japanese Patent Laid-open Publication (Tokkaisho) No.57-45510.

Furthermore, when the visible light photoelectric conversion device 9ais selected for carrying out the focus detection with visible light, thedisplay device DP displays information based on the signal |dF|, butwhen the infrared light photoelectric conversion device 9b is selectedfor carrying out the focus detection with infrared light, the displaydevice DP displays information based on the signal |dF-S|. Therefore, ineither cases, the objective lens can be so adjusted as to properly focusthe image for the visible light.

According to the block diagram shown in FIG. 1a, each interchangeablelens produces a data S (=dL-d/n) which is determined by the deflectiondL and distance d/n with an assumption that the distance d/n isconstant. If the distance d/n of one camera body is difference from theother camera body, and if the interchangeable lens is applicable to bothcamera bodies, it is necessary to change the data S with respect to thechange of the distance d/n. This can be accomplished by two differentways. The first way is to store a data dL to each interchangeable lens,and store a data d/n to each camera body, and by the use of data dL fromthe lens and d/n from the camera body, the required data S iscalculated. The second way is to store a data S to each interchangeablelens, in which S is equal to dL-d/n, wherein d/n is an optical distancefor the standard camera body. The camera body other than the standard isstored with a difference dP between the optical distance d/n for thestandard camera and its optical distance d/n. When the interchangeablelens is mounted on the standard camera body, the data S from the lens isused in the camera body without any change. But, when theinterchangeable lens is mounted on a non-standard camera body, the dataS from the lens is corrected using the difference dP.

Referring to FIG. 3, there is shown a first modification of the beamsplitter 7 described above. A beam splitter 7' shown therein includes aparallelepiped glass block 56, a triangle glass block 57, and amulti-film layer 58 sandwiched between blocks 56 and 57. The multi-filmlayer 58 is defined by twenty-three films deposited one over the otherby a suitable depositing method. The twenty-three films have refractiveindex and optical thickness as given in Table 1 below.

                                      TABLE 1                                     __________________________________________________________________________    Layer No.  1   2   3   4   5   6   7   8   9   10  11  12  13                 __________________________________________________________________________    Refractive Index n                                                                       1.38                                                                              2.30                                                                              1.38                                                                              2.30                                                                              1.38                                                                              2.30                                                                              1.38                                                                              2.30                                                                              1.38                                                                              2.30                                                                              1.38                                                                              2.30                                                                              1.38               Optical Thickness nd                                                                     0.32λ.sub.0                                                                0.25λ.sub.0                                                                0.25λ.sub.0                                                                0.25λ.sub.0                                                                0.25λ.sub.0                                                                0.25λ.sub.0                                                                0.25λ.sub.0                                                                0.25λ.sub.0                                                                0.25λ.sub.0                                                                0.25λ.sub.0                                                                0.25λ.sub.0                                                                0.25λ.sub.0                                                                0.25λ.su                                                               b.0                __________________________________________________________________________                Layer No.  14  15  16  17  18  19  20  21  22  23                 __________________________________________________________________________                Refractive Index n                                                                       2.30                                                                              1.38                                                                              2.30                                                                              1.38                                                                              2.30                                                                              1.38                                                                              2.30                                                                              1.38                                                                              2.30                                                                              1.38                           Optical Thickness nd                                                                     0.25λ.sub.0                                                                0.25λ.sub.0                                                                0.25λ.sub.0                                                                0.25λ.sub.0                                                                0.25λ.sub.0                                                                0.25λ.sub.0                                                                0.25λ.sub.0                                                                0.25λ.sub.0                                                                0.25λ.sub.0                                                                0.32λ.su                                                               b.0                __________________________________________________________________________     *Note: λ.sub.0 = 1100 nanometers                                  

It is to be noted that the glass blocks 56 and 57 have a refractiveindex of 1.5168. Of the twenty-three films in the multi-film layer 58,the films having a refractive index of 1.38 as shown in Table 1 are madeof MgF₂, and the films having a refractive index of 2.30 are made ofTiO₂ or CeO₂. When light rays hit on the junction face between the glassblocks 56 and 57 with an incident angle of 45°, as illustrated in FIG.3, rays in infrared region reflect with a high percentages, but rays invisible light region reflect with a low percentages, as shown in a graphof FIG. 4, wherein abscissa and ordinate represent, respectively,wavelength in nanometers and normalized reflectance Rf in percentages.More specifically, the reflectance is less than 10% within a visiblelight range, such as 460-660 nanometers, and is greater than 90% withinan infrared light range, such as 800-870 nanometers. Since twenty-threefilms of the multi-film layer 58 are made of dielectric material, suchas MgF₂ and TiO₂, or CeO₂, no light is absorbed in these films. Thus,the transmittance Tf of the rays through the junction can be given as:

    Tf≈100-(%).

Therefore, it can be said that the transmittance is greater than 90% ina visible light range, 460-660 nanometers, and is less than 10% in aninfrared light range, 800-870 nanometers. Thus, when the beam splitter7' is used, it is possible to divide the incident light into visiblelight and infrared light with almost no loss of light.

Referring to FIG. 5, there is shown a second modification of the beamsplitter 7 described above. A beam splitter 7" shown therein is aso-called half-mirror type defined by a base glass plate 60 and amulti-film layer 61 deposited on the base glass plate 60. The multi-filmlayer 61 has thirteen films deposited one over the other through asuitable depositing method. The thirteen films have refractive index andoptical thickness as given in Table 2 below.

                                      TABLE 2                                     __________________________________________________________________________    Layer No.  1   2   3   4   5   6   7   8   9   10  11  12  13                 __________________________________________________________________________    Refractive Index n                                                                       1.38                                                                              2.30                                                                              1.38                                                                              2.30                                                                              1.38                                                                              2.30                                                                              1.38                                                                              2.30                                                                              1.38                                                                              2.30                                                                              1.38                                                                              2.30                                                                              1.38               Optical Thickness nd                                                                     0.125λ.sub.0                                                               0.25λ.sub.0                                                                0.25λ.sub.0                                                                0.25λ.sub.0                                                                0.25λ.sub.0                                                                0.25λ.sub.0                                                                0.25λ.sub.0                                                                0.25λ.sub.0                                                                0.25λ.sub.0                                                                0.25λ.sub.0                                                                0.25λ.sub.0                                                                0.25λ.sub.0                                                                0.32λ.su                                                               b.0                __________________________________________________________________________     *Note: λ.sub.0 = 1000 nanometers                                  

It is to be noted that the base glass plate 60 has a refractive index of1.5168. Of the thirteen films in the multi-film layer 61, the filmshaving a refractive index of 1.38 as shown in Table 2 are made of MgF₂,and the films having a refractive index of 2.30 are made of TiO₂ orCeO₂. When light rays hit on the beam splitter 7" with an incident angleof 45°, as illustrated in FIG. 5, rays in infrared region reflect with ahigh percentages, but rays in visible light region reflect with a lowpercentages, as shown in a graph of FIG. 6, wherein abscissa andordinate represent, respectively, wavelength in nanometers andnormalized reflectance Rf in percentages. More specifically, thereflectance is very low (thus, transmittance is very high) in a visiblelight range, such as 400-700 nanometers, and is very high (thus,transmittance is very low) in an infrared light range, such as 800-1000nanometers.

Referring to FIG. 7, a major portion of the optical arrangement of thefocus detecting device employing the beam splitter 7" is shown. In FIG.7, 62 is a reflection mirror, 8' is an optical element having relaylenses 8'a and 8'b.

It is to be noted that the auto-focusing system according to the presentinvention can be arranged in different manner than the above describedarrangement.

For example, in the beam splitter 7 shown in FIGS. 1a and 1b, the secondreflecting face 7b can be so arranged as to have reflectance andtransmittance characteristic varied with respect to wavelength in asimilar manner to the first reflecting face 7a. More specifically, thesecond reflecting face 7b can be so arranged as to have a normalizedreflectance as shown by a dot-dash line in FIG. 2a. When this is done,the range in which the infrared light photoelectric conversion device 9breceives light is narrowed. Accordingly, the wavelength of light thatcan be detected by the infrared light photoelectric conversion device 9bis limited to a certain narrow range, resulting in preciseness of thedeflection dL. Thus, the correction using the deflection dL (or data S)can be done with a high accuracy. Also, in a case where an auxiliarylight is emitted, an infrared LED or infrared laser having intense beamwith a high reflectance to the first and second reflecting faces 7a and7b should be used, thereby improving the accuracy of the correctionusing deflection dL (or data S). In this case, it is preferable toprovide a light absorber at left end surface, when viewed in FIG. 1b, ofthe beam splitter 7, so that the lights which have passed through thesecond reflecting face 7b will not reflect back on such an end surface.

Also, in the above description, a beam splitter having a hightransmittance of visible light and a high reflectance of infrared lightis used. But instead, a beam splitter having a high reflectance ofvisible light and a high transmittance of infrared light can be used.

Furthermore, a beam splitter having three reflecting faces can be used.In this case, the first reflecting face reflects infrared lights andtransmits visible lights. The second reflecting face receives theinfrared lights reflected from the first reflecting face and reflectsinfrared lights having a wavelength of a first particular range, andtransmits infrared lights having a wavelength of a second particularrange. The third reflecting face receives and reflects the infraredlights having a wavelength of the second particular range. In this case,two infrared light photoelectric conversion devices should be provided:one for receiving the infrared lights from the second reflecting face;and the other for receiving the infrared lights from the thirdreflecting face.

Referring to FIGS. 8a and 8b, a circuit diagram of the auto-focusingsystem according to one embodiment of the present invention is shown, inwhich characters A-E in circle in FIG. 8a are connected to correspondingcharacters in circuit in FIG. 8b.

A reference character IRD at upper left corner of FIG. 8a is aphotoelectric conversion element for monitoring infrared lights, and VSDis a photoelectric conversion element for monitoring visible lights. Thephotoelectric conversion element IRD is provided in the infrared lightphotoelectric conversion device 9b, shown in FIG. 1a or 1b, and thephotoelectric conversion element VSD is provided in the visible lightphotoelectric conversion device 9a. These photoelectric conversionelements IRD and VSD are coupled with operational amplifiers OA1 and OA2and logarithmic compression diodes D1 and D2, thereby defining lightmeasuring circuits. The outputs of the operational amplifiers OA1 andOA2 are compared with each other in a comparator AC1. When the outputfrom the amplifier OA1 is greater than that from the amplifier OA2,i.e., when the infrared lights are stronger than the visible lights, thecomparator AC1 produces HIGH, and when the output from the amplifier OA2is greater than that from the amplifier OA1, i.e., when the visiblelights are stronger than the infrared lights, the comparator AC1produces LOW.

The output of the operational amplifier OA1 is also compared with areference voltage from a constant voltage source CE2 by a comparatorAC3. When the output from the operational amplifier OA1 representing theinfrared light level is smaller than the reference voltage from thevoltage source CE2, the comparator AC3 produces HIGH. But, when theoutput from the amplifier OA1 is greater than the reference voltage fromthe voltage source CE2, the comparator AC3 produces LOW.

Likewise, the output of the operational amplifier OA2 is also compared areference voltage from a constant voltage source CE1 by a comparatorAC2. When the output from the operational amplifier OA2 representing thevisible light level is greater than the reference voltage from thevoltage source CE1, the comparator AC2 produces HIGH. But, when theoutput from the amplifier OA2 is smaller than the reference voltage fromthe voltage source CE1, the comparator AC2 produces LOW.

A logic circuit defined by inverter IN1, AND gates AN1 and AN2 and ORgates OR1 and OR2 receives the outputs from three comparators AC1, AC2and AC3 and selects which one of the two outputs from photoelectricconversion devices 9a and 9b should be used, and determines whether ornot an infrared LED for the auxiliary light should be actuated to emitinfrared light for the focus detection. A detail of operation of thelogic circuit is shown below in Table 3.

                                      TABLE 3                                     __________________________________________________________________________    Output levels of                         Selected                                                                           Infra-                          Photoelectric                            Element                                                                            red LED                         Conversion Ele-                          IRD or                                                                             IRL ON                          ments IRD & VSD  AC1                                                                              AC2                                                                              AC3                                                                              IN1                                                                              AN1                                                                              AN2                                                                              OR1                                                                              OR2                                                                              VSD  or OFF                          __________________________________________________________________________    1 IRD>VSD+IRD>CE2                                                                              H  φ                                                                            L  L  L  L  L  H  IRD  OFF                             2 IRD>VSD+IRD<CE2                                                                              H  φ                                                                            H  L  L  H  H  H  IRD  ON                              3 VSD>IRD+VSD>CE1                                                                              L  L  φ                                                                            H  L  L  L  L  VSD  OFF                             4 VSD>IRD+VSD<CE1                                                                              L  H  φ                                                                            H  H  L  H  H  IRD  ON                              __________________________________________________________________________     NOTE:                                                                         (1) + means "at the same time".                                               (2) φ means "either H or L".                                         

As understood from Table 3, row 1, when the output level ofphotoelectric conversion element IRD is greater than that from theelement VSD and, at the same time, greater than the reference voltagefrom the voltage source CE2, comparators AC1 and AC3 produces HIGH andLOW, respectively. Thus, the AND gate AN2 produces LOW, and the inverterIN1 produces LOW, thereby producing LOW from the AND gate AN1.Furthermore, OR gate OR1 produces LOW and OR gate OR2 produces HIGH.Thus, when a data flip-flop DF1 receives a clock pulse, its Q outputproduces LOW. Thus, an AND gate AN3 produces LOW to turn off transistorBT1. As a result, the infrared LED IRL is maintained OFF. Moreover, whena data flip-flop DF2 receives a clock pulse, its Q output produces HIGH,and its Q output produces LOW, thus turning an analog switches AS1 andAS4 on, permitting the transmission of signal from a CCD (charge coupleddevice) IRC provided in the infrared light photoelectric conversiondevice 9b, and turning an analog switches AS2 and AS3 off, cuttingsignal from a CCD VSC provided in the visible light photoelectricconversion device 9a.

The operation shown in Table 3 under other rows is similar to thatdescribed above.

As apparent from Table 3, rows 1 and 2, when ever the output level ofinfrared light photoelectric conversion element IRD is greater than thatfrom the visible light photoelectric conversion element VSD, infraredlight photoelectric conversion device 9b is selected. In this case, ifthe output level of infrared light photoelectric conversion element IRDis lower than a predetermined level (row 2), the infrared LED IRL isactuated to emit auxiliary light of infrared rays.

Contrary, the visible light photoelectric conversion device 9a isselected only when the output level of visible light photographicconversion element VSD is greater than that from the infrared lightphotoelectric conversion element IRD and, at the same time, greater thana predetermined level (row 3). When the output level of visible lightphotographic conversion element VSD is greater than that from theinfrared light photoelectric conversion element IRD, but less than thepredetermined level (row 4), the infrared light photoelectric conversiondevice 9b is selected and, at the same time, the infrared LED IRL isactuated to emit auxiliary light of infrared rays.

A further detail of the circuit shown in FIG. 8a will become apparentfrom the following description.

The output of the OR gate OR1 is connected to D input of data flip-flopDF1, and the output of the OR gate OR2 is connected to D input of dataflip-flop DF2. Each of the data flip-flops DF1 and DF2 has a clockterminal CL which is connected to an output O3 of a microcomputer MCO(FIG. 8b). When the microcomputer MCO produces from its output O3 astart measuring signal for effecting the start of light measuring forthe focus detection, data flip-flops DF1 and DF2 latches the data attheir D input.

Still referring to FIG. 8a, a reference character COT designates acontroller for controlling the light measuring operation for the focusdetection, IRC is a CCD provided in the infrared light photoelectricconversion device 9b, and VSC is a CCD provided in the visible lightphotoelectric conversion device 9a. These CCDs IRC and VSC are providedfor the focus detection. A sample-and-hold circuit SH is provided forholding analog signal from either CCD IRC or VSC, and ananalog-to-digital converter AD is provided for converting an output ofsample-and-hold circuit SH from analog to digital form.

When the start measuring signal, which is a pulse, is applied fromoutput O3 of microcomputer MCO to input ST of controller COT, thecontroller COT produces from its output θR a reset pulse which isapplied to each of analog switches AS5 and AS6, thereby turning theanalog switches AS5 and AS6 on. By the turn on of the analog switchesAS5 and AS6, each of the CCDs IRC and VSC are charged through terminalsIAD and VAD up to a level equal to a constant voltage source CE5. Theoutput .0.R is also connected to a set terminal S of a flip-flop FF1.Thus, by a reset pulse produced from the output .0.R, the flip-flop FF1is turned to set condition, thereby producing HIGH from Q output of theflip-flop FF1. This HIGH is applied to AND gate AN3, and if the dataflip-flop DF1 is producing HIGH at this moment, the AND gate AN3produces HIGH, thereby conducting transistor BT1. Thus, the LED IRLemits infrared beams.

The CCDs IRC and VSC receive signals from their own light receivingelements, charge the signals, and produce gradually-increasing voltagesignals representing the charged amount in each CCD from their outputsIAD and VAD. In this case, when the data flip-flop DF2 is producing HIGHfrom its Q output (meaning that CCD IRC of infrared should be used),analog switch AS4 conducts to transmit voltage signal from output IAD ofCCD IRC to comparator AC4. On the other hand, when the Q output offlip-flop DF2 is producing HIGH, analog switch AS3 conducts to transmitvoltage signal from output VAD of CCD VSC to comparator AC4.

The comparator AC4 compares the gradually increasing voltage signal fromoutput IAD or VAD with a reference voltage from a constant voltagesource CE3, and when the voltage signal reaches the reference voltagefrom the voltage source CE3, it produces HIGH which is applied tocontroller COT. Thereupon, the controller COT produces a transmissionpulse from its output .0.T, thereby shifting the charge stored in eachCCD IRC or VSC to transmission gate. The transmission pulse is alsoapplied to reset terminal R of flip-flop FF1, thereby resetting theflip-flop FF1. Thus, the LED IRL for the auxiliary light stops theinfrared light emission. Thereafter, output terminal IRS or VSS of CCDIRC or VSC continuously produce stored charge in accordance withtransmission clocks from outputs .0.1, .0.2 and .0.3. In this case, whenthe data flip-flop DF2 is producing HIGH from its Q output, analogswitch AS1 conducts to transmit the signal representing the receivedinfrared light from output IRS to sample-and-hold circuit SH. But, whenthe data flip-flop DF2 is producing HIGH from its Q output, analogswitch AS2 conducts to transmit the signal representing the receivedvisible light from output VSS to sample-and-hold circuit SH.

The controller COT produces from its terminal .0.S a pulse for effectingthe sample-and-hold operation in the circuit SH and, thereafter,produces a pulse from its terminal .0.C to AD converter AD for effectinganalog-to-digital conversion. Then, controller COT produces from itsoutput TR a pulse to an input i4 of microcomputer MCO for the indicationthat the data transmission will be carried out. Thereupon, the ADconverted data by the AD converter AD is transmitted from controller COTto microcomputer MCO through its inut port IP1. Thereafter, the abovedescribed series operation of producing stored charge, sample-and-hold,AD conversion; and data transmission is repeated for a number of timesequal to the number of light receiving element in CCD IRC or VSC. Whenrepeated for the required number of times, the controller COT producesfrom its output EN a pulse indicating the completion of transmission toan input i6 of microcomputer MCO, thereby stopping the repetition.

According to the above description, the determination of which one ofthe two CCDs should be selected and the determination of whether or notto turn on the LED IRL are carried out by the use of photoelectricconversion elements IRD and VSD. But, both determinations can be donewithout such elements IRD and VSD. For example, before carrying out thelight measuring for the focus detection, the CCDs IRC and VSC areactuated to store charges corresponding to the infrared and visiblelights, respectively, and the voltage signals representing the chargedamounts, as produced from the outputs IAD and VAD, can be used as outputsignals from the elements IRD and VSD, or from the amplifiers OA1 andOA2 if such voltage signals have enough high amplitude.

Referring particularly to FIG. 8b, the autofocusing system furtherincludes a battery BA for supplying D.C. power and a manually operableswitch MS, such as one provided in association with a shutter releasebutton (not shown) and closes upon depression to a half-way down. Theswitch MS is connected to an inverter IN2 which, when the switch MS isturned on, produces HIGH, thereby starting the microcomputer MCO tocarry out the focus condition detection and focus adjustment and, at thesame time, starting a light measuring, calculation and display circuitLM. Also, in response to the closure of the switch MS, the microcomputerMCO produces HIGH from its output 01, thereby producing LOW from aninverter IN3 to turn a transistor BT2 to a conductive state. Thus, D.C.power is supplied to line Vcc.

Another manually operable switch RS is provided, for example inassociation with a shutter release button, and closes upon depression toits full way. When the switch RS closes, an inverter IN4 produces HIGH.In this case, if an exposure control circuit EC is in a preparatorycondition and an inverter IN0 is producing HIGH, AND gate AN0 producesHIGH, thereby stopping the microcomputer to further carry out the focuscondition detection and focus adjustment. Then, it is waited until theexposure control stops. Also, when the switch RS closes, the exposurecontrol circuit EC carries out an exposure control operation based onexposure control values from the light-measuring, calculation anddisplay circuit LM. When the exposure control operation completes, theexposure control circuit EC produces HIGH indicating the completion ofoperation, and applies it to input i1 of the microcomputer MCO. Theexposure control circuit EC produces LOW when an exposure controlarrangement has completed its charge and when the preparation for theexposure control operation is completed.

A display device DP receives data from an output port OP1 of themicrocomputer MCO and displays either one of in-focus, near-focus andfar-focus. A motor drive circuit MDR receives data from an output portOP2 and drives a motor MO either in forward or backward direction,thereby operating a lens drive mechanism LDR to shift the lens to anin-focus position. An encoder EN is coupled to lens drive mechanism LDRfor producing a pulse each time the lens is shifted for a predeterminedunit distance. An interface circuit IF is provided, which takes datanecessary for driving the lens from a data producing circuit LDO inresponse to a pulse from output 02 of microcomputer MCO. The dataproducing circuit LDO, provided in the interchangeable lens mounted on acamera body, supplies the data S (or data dL) and data K representingthe rate of lens shift with respect to a predetermined number of pulsesproduced from the encoder EN.

Next, a detail of the interface circuit IF and data producing circuitLDO is described with reference to FIGS. 9a and 9b, wherein terminals J1to J4 provided in a camera body are connectable to correspondingterminals J1' to J4' provided in an interchangeable lens.

Referring particularly to FIG. 9a, when microcomputer MCO produces HIGHfrom its output 02, a flip-flop FF5 is set, thereby producing HIGH fromQ output of flip-flop FF5. Then, when a clock terminal CL of dataflip-flop DF5 receives a clock pulse from oscillator OSC, the dataflip-flop DF5 produces HIGH from its Q output. Accordingly, an AND gateAN10 is enabled to transmit a train of clock pulses from oscillator OSCto clock terminal CL of a ring counter CO1. In response to each clockpulse, the ring counter CO1 counts up. More specifically, when the ringcounter CO1 has counted one clock pulse, it produces HIGH from itsoutput b0 and produces LOW from the rest of its outputs; when it hascounted two clock pulses, it produces HIGH from its output b1 andproduces LOW from the rest of its outputs; when it has counted ten clockpulses, it produces HIGH from its output b9 and produces LOW from therest of its outputs; when it has counted eleven clock pulses, itproduces HIGH from its output b0 and produces LOW from the rest of itsoutputs; and so on.

Referring also to FIG. 9b, the Q output of data flip-flop DF5 is alsoconnected through terminals J1 and J1' to the circuit provided in themounted interchangeable lens. More specifically, the terminal J1' isconnected to a latch circuit LA3 which upon receipt of HIGH from the Qoutput of data flip-flop DF5, latches 5-bit data representing a distancebetween the object to be photographed and the camera from a focusdistance reading device DD through analog switches AS15-AS19. The focusdistance reading device DD reads the distance between the object to bephotographed and the camera by detecting the shifted position of beobjective lens. The terminal J1' is also connected to a delay circuit DLwhich after a predetermined period from the receipt of HIGH from the Qoutput of data flip-flop DF5, produces HIGH which is inverted to LOW byan inverter IN10. The HIGH from the delay circuit DL is applied toanalog switches AS10-AS15 to turn on the same, and LOW from the inverterIN10 is applied to analog switches AS15-AS19 to turn off the same. Thus,when a HIGH is produced from the delay circuit DL, a decoder DE receives10-bit signal (5-bit distance data from the latch LA3 and 5-bit focallength data from a focal length setting circuit FD) which is convertedto 6-bit signal and applied to a ROM RO at its least significant sixbits.

In FIG. 9b, the focus distance reading device DD and focal lengthsetting device FD are each formed by a coded plate (not shown) and aportion enclosed by a dot-dash line can be formed in a single IC chip.According to the arrangement shown in FIG. 9b, it is possible totransmit 10-bit signal from the devices DD and DF to the IC chip throughonly six lines: five lines extending from the latch LA3; and one lineextending from the delay circuit DL, resulting in fewer connectionsbetween the IC chip and its associated circuit. Furthermore, the circuitshown in FIG. 9b is particularly designed for the employment in aninterchangeable lens having data S (or data dL) and data K which varywith respect to the change of focusing distance and focal length.Therefore, signals representing these two variants as produced from thedevices DD and FD are converted by the decoder DE into 6-bit signal tobe applied to the ROM RO at its least significant six bits.

Moreover, the Q output of data flip-flop DF5 is connected throughterminals J1 and J1' to AND gate AN14. Thus, the AND gate AN14 isenabled upon receipt of HIGH from the data flip-flop DF5, therebypermitting the supply of clock pulses from the oscillator (FIG. 9a)through the terminal J2 and J2' to a ring counter CO2, which operates inthe same manner as the above-described ring counter CO1.

When the ring counter CO1 receives second clock pulse to its clockterminal CL, it produces HIGH from its output b1 for the first time.Accordingly, a counter CO3 (FIG. 9b) connected to the output b1 of thecounter CO1 through terminals J3 and J3' counts up to one, therebyproducing a 2-bit signal "01" from its outputs Q1 and Q2. These outputsQ1 and Q2 of the counter CO3 are connected to two most significant bitterminals of ROM RO. Thus, in this case, the ROM RO receives an 8-bitsignal "01XXXXXX" (XXXXXX is a 6-bit output from decoder DE.) which isan address for designating a location in ROM RO where data S (or dL)corresponding to the detected focus distance and set focal length isstored. Then, when output L2 of ring counter CO2 produces HIGH, thedesignated data S (or dL) defined by a plurality of bits, such as 8bits, in ROM RO is transferred parallelly to a shift register SR2.Thereafter, in a synchronized relation with the clock pulses from theterminal J2', the data S (or dL) is sent out bit-by-bit in response tothe positive edge of each clock pulse from a terminal OUT of the shiftregister SR2, and is transferred though the terminals J4' and J4 to ashift register SR1 provided in interface circuit IF in a camera body.The shift register SR1 stores the data S (or dL) bit-by-bit in responseto the negative edge of each clock pulse from the oscillator OSC.Therefore, the storing of the data S (or dL) in the shift register SR1starts synchronized relation to the negative edge of a pulse producedfrom terminal b2 of the ring counter CO1 and ends in synchronizedrelation to the negative edge of a pulse produced from terminal b9 ofthe ring counter CO1.

Thereafter, when terminal b0 of the ring counter CO1 produces HIGH forthe second time, a data flip-flop DF7 produces HIGH from its Q output.At this moment, a data flip-flop DF8 is producing HIGH from its Qoutput, an AND gate AN11 is enabled to produce HIGH from terminal b0 ofring counter CO1. And, in response to the positive edge of HIGH producedfrom AND gate AN11, a latch LA1 stores data S (or dL) from shiftregister SR1.

Then, while terminal b1 of the ring counter CO1 is producing HIGH forthe second time, this HIGH is applied through terminals J3 and J3' tocounter CO3 which then produces "10" from its outputs Q1 and Q2. Thus,in this case, the ROM RO receives an 8-bit signal "10XXXXXX" which is anaddress for designating a location in ROM RO where data K correspondingto the read focus distance and set focal length is stored. Then, inresponse to the positive edge of a pulse produced from output L2 of ringcounter CO2, the designated data K is transferred to shift register SR2.Thereafter, in a synchronized relation with the clock pulses from theterminal J2', the data K is sent out bit-by-bit in response to thepositive edge of each clock pulse from a terminal OUT of the shiftregister SR2, and is transferred though the terminals J4' and J4 to ashift register SR1 provided in interface circuit IF in a camera body.The shift register SR1 stores the data K bit-by-bit in response to thenegative edge of each clock pulse from the oscillator OSC. Therefore,the storing of the 8-bit data K in the shift register SR1 starts insynchronized relation to the negative edge of a pulse produced fromterminal b2 of the ring counter CO1 and ends in synchronized relation tothe negative edge of a pulse produced from terminal b9 of the ringcounter CO1.

Thereafter, when terminal b0 of the ring counter CO1 produces HIGH, adata flip-flop DF8 produces HIGH from its Q output. Therefore, an ANDgate AN12 is enabled to produce HIGH from terminal b0 of ring counterCO1. And, in response to the positive edge of HIGH produced from ANDgate AN12, a latch LA2 stores data K from shift register SR1. The HIGHfrom AND gate AN12 is also applied through an OR gate OR10 to resetterminal of each of flip-flop FF5, data flip-flops DF5, DF6, DF7 and DF8and ring counter CO1, thereby resetting these circuits. When the dataflip-flop DF5 is reset, its Q output produces LOW which is appliedthrough terminals J1 and J1' and OR gate OR11 to reset terminal of eachof counters CO2 and CO3, thereby resetting these counters.

The above described operation is carried out to provide necessary data S(or dL) and data K to the interface circuit IF of the camera body, andthrough input ports IP2 and IP3 to microcomputer MCO. And, whenever thecondition of focus distance or focal length changes, the above describedoperation is repeated to renew the necessary data S (or dL) and data K.

In FIGS. 9a and 9b, reference characters PO1 and PO2 designatepower-on-reset circuit, and each produces a reset signal when a power issupplied from a power supply line Vcc in response to the conduction oftransistor BT2. The reset signal produced from the power-on-resetcircuit PO1 is applied to OR gate OR10, and in response to the negativeedge of the reset signal, each of flip-flop FF5, data flip-flops DF5,DF6, DF7 and DF8 and ring counter CO1 is reset. And, the reset signalproduced from the power-on-reset circuit PO2 is applied to OR gate OR11,and in response to the negative edge of the reset signal, each ofcounters CO2 and CO3 is reset.

Referring to FIG. 10, a circuit which is a modification of the circuitof FIG. 9b is shown, and is arranged such that the data S (or dL) anddata K vary with respect to the change of either one of focus distanceor focal length. According to the circuit shown in FIG. 10, the ROM ROhas its two most significant bits of 8-bit inputs connected to counterCO3, the least significant bit connected to ground, and the remainingfive bits connected to focus distance measuring device DD or focallength setting device FD, which ever is provided in the circuit. Theremaining parts and the operation of the circuit of FIG. 10 is similarto that described above in connection FIG. 9b.

Referring to FIG. 11, a circuit which is a further modification of thecircuit of FIG. 9b is shown. According to this modification, a circuitDIA defined by diode arrays is provided in place of ROM RO. When outputQ2 of counter CO3 produces HIGH, a diode array provided in circuit DIAand connected to the output Q2 is so actuated as to produce a signalrepresenting data S (or dL). And, when output Q1 of counter CO3 producesHIGH, another diode array provided in circuit DIA and connected to theoutput Q1 is so actuated a to produce a signal representing data K. Theremaining circuit of FIG. 11 is the same as that shown in FIG. 9b.

Next, the operation of the circuit of FIGS. 8a and 8b will be describedwith reference to a flow chart of FIGS. 12a and 12b. While the manualswitch MS is turned off, microcomputer MCO is in a "HALT" conditionconsuming a very low electric power. When the switch MS is turned on, aHIGH produced from inverter IN2 is applied to an interruption terminal10, whereby the microcomputer MCO starts to operate from step #0. Atstep #0, a HIGH is produced from output terminal 01, thereby producing aLOW from inverter IN3. Thus, transistor BT2 conducts to supply electricpower to power supply line Vcc. Then, at step #1, it is discriminatedwhether or not switch RS is turned on, by the discrimination of signalat the input i3. When the switch RS is turned off, input i3 receives LOWfrom inverter IN4 through AND gate AN0. But if switch RS is turned on,input i3 receives HIGH from inverter IN4. When input i3 is receivingHIGH, i.e., when switch RS is on, the program advances to step #41 forthe exposure control as will be described later. Contrary, when input i3is receiving LOW, i.e., when switch RS is off, output 03 produces HIGH,at step #2 for starting the light measuring operation for the focusdetection. Then, at step #3, output 02 produces HIGH to fetch data S (ordL) and data K from the mounted interchangeable lens.

Then, at step #4, it is waited until input i4 receives HIGH. When inputi4 receives HIGH, data (of A-D converted value of charge in CCD VSC orIRC by one light receiving element) from controller COT is read intomicrocomputer MCO through input port IP1, at step #5. At step #6, it isdiscriminated whether input i6 is receiving HIGH. If input i6 isreceiving LOW, the program returns back to step #4 for reading next data(of A-D converted value of charge in CCD VSC or IRC by another lightreceiving element). Contrary, if input i6 is receiving HIGH, as occurredwhen data of A-D converted value of charge in CCD VSC or IRC by all thelight receiving elements is read in, the program advances to step #7. Atstep #7, it is discriminated whether or not input i3 is receiving HIGH,in the same manner as step #1. If input i3 is receiving HIGH, theprogram jumps to step #41. If not, then the program proceeds to step #8.At step #8, data S (or dL) is read in through input port IP2, and atstep #9, data K is read in through input port IP3. Then, at step #10, anamount of defocus (out of focus) of the image formed on a CCD, and alsoa direction of defocus are calculated using data received through inputport IP1. A manner for carrying out this calculation is disclosed, forexample, in U.S. Pat. No. 4,333,007 patented June 1, 1982 to Langlais etal., or in Japanese Patent Laid-open Publication (Tokkaisho) No.57-45510.

Then, at step #11, it is discriminated whether input i5 is receivingHIGH or not. If input i5 is receiving HIGH, it is understood that thedefocus signal dF (representing the amount and direction of defocus) iscalculated using output from CCD IRC provided in the infrared lightphotoelectric conversion device 9b. Therefore, microcomputer MCO carriesout a calculation:

    K·(dF-dL)=N

using deflection data dL for correcting defocus signal dF and rate Kwhich are obtained from ROM RO.

If input i5 is not receiving HIGH, it is understood that the defocussignal dF is calculated using output from CCD VSC provided in thevisible light photoelectric conversion device 9a. In this case,microcomputer MCO carries out a calculation:

    K·dF=N

using defocus signal dF without correction and rate K.

It is to be noted that the calculated result N in the above twoequations indicates a number of pulses to be produced from encoder EN toshift the mounted lens to the properly infocused position.

Then, at step #14, the focus condition is indicated through displaydevice DP. And, at step #15, it is discriminated whether or not input i3is receiving HIGH for discriminating whether the switch RS is turned onor not, in the same manner described above. At step #16, it isdiscriminated whether the number N is equal to zero or not. If it iszero, the program jumps to step #38, which will be described later. Ifnot, the program advances to step #17 for setting the number N inregister M in microcomputer MCO. Then, at step #18, motor drive circuitMDR is actuated to start motor MO in forward or backward directiondetermined by dF, and then a data PO is set up in a register P inmicrocomputer MCO, at step #19. Then, it is discriminated at step #20whether or not input i2 receives HIGH pulse from encoder EN. If inputhas received HIGH, the program advances to step #21, and if not,advances to step #27.

At step #27, it is discriminated whether or not input i3 is receivingHIGH to discriminate whether switch RS is closed or not. If input i3 isreceiving HIGH, it is understood that an exposure control operation willbe carried out. In this case, motor MO is stopped at step #31, and aflag JF in microcomputer MCO is reset, and then, the program advances tostep #41. Contrary, if input i3 is receiving LOW, "1" is subtracted fromthe content of register P (step #28) and, thereafter, it isdiscriminated whether the content of register P is zero (step #29). Ifnot equal to zero, the program advances to step #30 at which it isdiscriminated whether flag JF is carrying zero or not. If flag JF iscarrying zero, the program returns to step #20 to repeat thediscrimination whether input i2 receives HIGH pulse from encoder EN.But, if the flag JF is notcarrying zero, the program advances to step#25 at which it is discriminated whether or not input i2 is receivingLOW. If input i2 is receiving LOW, the program again goes to step #27.The above operation is repeatedly carried out until input i2 receivesHIGH. If input i2 fails to receive HIGH before the content of theregister P becomes zero, i.e., before a predetermined period of time, itis understood that the lens is unable to move any further because it isalready shifted to one extreme end. In this case, motor MO is stopped atstep #33, and a warning is displayed (step #34). Then, flag JF is resetat step #35 and then program advances to step #38.

Returning back to step #20, if input i2 receives a HIGH pulse fromencoder EN, the content of the register M, which is now N, is subtracted"1" (step #21). Then, it is discriminated whether the content of theregister is equal to zero or not (step #22). If not, "1" is set in flagJF (step #23) and a data PO is set up in register P (step #24). Then, itis discriminated whether input i2 receives LOW, i.e., whether the HIGHpulse ends or not (step #25). If it is discriminated that the HIGH pulsehas ended, the program advances to step #26 to reset flag JF and,thereafter, it returns back to step #19.

In the foregoing description, the content of register M is subtracted by"1" only when it is discriminated that input i2 receives HIGH, i.e., inresponse to the positive edge of a pulse from encoder EN. Instead,according to one modification, the number N may be doubled and thecontent of register M is subtracted by "1" also when it is discriminatedthat input i2 receives LOW, i.e, in response not only to the positiveedge, but also to the negative edge of a pulse from encoder EN. In thiscase, a discrimination step same as the step #22 should be added betweensteps #25 and #26 for the discrimination whether the content of theregister M is equal to zero or not. If it is equal to zero, the programadvances to step #36, as in the case of step #22 to end the lensadjustment, as will be described below. When this modification isemployed, the lens position can be adjusted more precisely to theinfocus position.

At step #22, if it is discriminated that the content of register M isequal to zero, it is understood that the lens is shifted to the infocusposition. Therefore, at step #36, motor MO is stopped and, at step #37,it is indicated through display device DP that the lens is shifted tothe infocus position.

At step #38, it is discriminated whether manual switch MS is on or not,by the discrimination of whether input i7 is receiving HIGH or not. Ifinput i7 receives HIGH as occurs when manual switch MS turns on, theprogram returns back to step #1 to repeat the above described operation.Contrary, if input i7 receives LOW, display device DP is turned off atstep #39 and LOW is produced from output 01 to turn transistor BT2 off,thereby cutting the supply of electric power to power supply line Vcc,and returning microcomputer MCO again to "HALT" condition. Also, if itis discriminated at step #1 that switch RS is turned off, it is waitedat step #41 until input i1 receives HIGH. Then, after completing theexposure control operation and when input i1 receives HIGH pulse fromexposure control circuit EC, the program advances to step #38.

Next, the description is directed to modifications of the abovedescribed embodiment.

As mentioned before, the photoelectric conversion element for the focusdetection can be formed by diode arrays which respond immediately to thelight, instead of an integration type which respond gradually to thelight, such as ROM RO.

Also, according to the above description, the data dF is calculatedusing digital value, which is an A/D converted value of output signalfrom photoelectric conversion element. Instead, it is possible tocalculate the data dF using analog value from the photoelectricconversion element, and the calculated result may be converted todigital form for the motor control and display.

Referring to FIG. 13, another embodiment of the present invention isshown. According to this embodiment, the photoelectric conversionelements IRD and VSD are eliminated, and CCDs IRC and VSC are used forobtaining signals which determine whether to use the auxiliary light, ornot, and which determine which one of the two signals from CCDs IRC andVSC is to be used.

A counter CO10 is reset by a reset pulse .0.R, counts up by clock pulse.0.1, and produces a pulse from its carry terminal after, e.g., 40 msec.When this pulse is produced, the signals produced from outputs IAD andVAD from CCDs IRC and VSC are compared with each other in comparatorAC10 and are each compared with a reference voltage from constantvoltage source CE10 in comparators AC11 and AC12, and the comparedsignals are applied to logic circuit defined by AND gates AN21 and AN32and inverter IN20. Furthermore, the outputs from AND gates AN21 and AN32are stored in data flip-flops DF20 and DF21.

If the compared results are such that IAD is smaller than VAD (meaningthat the infrared light is stronger than visible light) and IAD issmaller than a predetermined level CE10 (meaning that the infrared lightis stronger than a predetermined level), or that IAD is equal to orgreater than VAD (meaning that the infrared is not stronger than visiblelight) and VAD is weaker than the predetermined level CE10 (meaning thatvisible light is stronger than the predetermined level), both AND gatesAN21 and AN22 produce LOW, thereby storing LOW in both data flip-flopsDF20 and DF21. In this case, OR gate OR21 continues to produce LOW,thereby preventing LED IRL from emitting infrared light. In the abovegiven situation, since both outputs from CCDs IRC and VSC reach thepredetermined level CE10 before counter CO10 counts the time, e.g., 40msec, the charge to CCDs can be completed within a predetermined periodof time, such as 80 msec.

Contrary, if the compared results are such that IAD is smaller than VAD(meaning that the infrared light is stronger than visible light) and IADis equal to or greater than a predetermined level CE10 (meaning that theinfrared light is not stronger than a predetermined level), or that IADis equal to or greater than VAD (meaning that the infrared is notstronger than visible light) and VAD is equal to or greater than thepredetermined level CE10 (meaning that visible light is not strongerthan the predetermined level), both AND gates AN21 and AN22 produceHIGH, thereby storing LOW in both data flip-flops DF20 and DF21. In thiscase, OR gate OR21 produces HIGH, thereby emitting infrared light fromLED IRL. In the above given situation, an infrared light is emittedbecause, if CCD continues to charge without an auxiliary infrared light,the charging may not complete within a predetermined period of time,such as 80 msec., resulting in a long period of time for the focusdetection.

When a signal level from outputs IAD or VAD reaches the referencevoltage level of constant voltage source CE11, comparator AC13 or AC14produces HIGH, thereby producing a HIGH pulse from one-shot circuit OS10or OS11. Before producing a HIGH pulse from one-shot circuit OS10 orOS11, flip-flops FF10 and FF11 are both in reset condition. Therefore, aQ terminal of each flip-flop FF10 or FF11 is producing HIGH, therebyenabling AND gates AN24 and.AN23.

When a HIGH pulse is produced from one-shot circuit OS10, it istransmitted through OR gate OR22 and AND gate AN23 to flip-flop FF10,thereby changing the flip-flop FF10 to set condition. Accordingly,flip-flop FF10 produces HIGH from its Q output which is applied tocontroller COT though OR gate OR23 and also to analog switch AS1, andLOW from its Q output which is applied to AND gate AN24, therebydisabling AND gate AN24 to cut any HIGH pulse from one-shot circuitOS11. Thus, flip-flop FF11 continues to produce LOW from its Q outputand HIGH from its Q output. This condition is maintained until a resetpulse is produced from output 03 of microcomputer MCO.

Contrary, when a HIGH pulse is produced from oneshot circuit OS11,flip-flop FF11 is turned to set condition and flip-flop FF10 ismaintained in reset condition, thereby providing HIGH to controller COTand analog switch AS2.

In the above described operation, when controller COT receives HIGH fromOR gate OR23, controller COT produces a transmission pulse .0.T which isapplied to CCDs VSC and IRC. Furthermore, in the above operation, whenHIGH is applied to analog switch AS1, CCD IRC is selected for use infocus detection, and when HIGH is applied to analog switch AS2, CCD VSCis selected for use in focus detection. In this way, a CCD which ischarged to a predetermined level first is selected to be used in focusdetection.

An output of OR gate OR23 is also connected to a one-shot circuit OS12which produces a HIGH pulse when OR gate OR23 produces HIGH. The HIGHpulse from one-shot circuit OS12 is transmitted through OR gate OR24 toa reset terminal of data flip-flops DF20 and DF21. Accordingly, if LEDhas been emitting infrared light, the light emission stops when dataflip-flops DF20 and DF21 resets.

A counter CO11 is reset by a reset pulse .0.R from controller COT, andcounts a predetermined period of time, such as 80 msec., by the count ofclock pulses .0.1 and produces a pulse from its carry terminal whencounting has completed. If both comparators AC13 and AC14 are producingLOW at a moment when a pulse is produced from the counter CO11, thepulse from the counter CO11 is applied through OR gate OR22 and AND gateAN23 to set terminal of flip-flop FF10. Thus, flip-flop FF10 producesHIGH from its Q output, thereby actuating the controller COT to producea transmission pulse .0.T and, at the same time, selecting CCD IRCprovided in the infrared light photoelectric conversion device 9b. Theabove described operation is carried out when the object is relativelydark such that CCD fails to charge up to a predetermined level within 80msec. In this case, the charging is forcibly ended at the end ofcounting 80 msec. Furthermore, since LED IRL emits infrared light underthis operation, it is more likely that CCD IRC for the infrared lightproduces a higher output level than that from CCD VSC for the visiblelight. Therefore, under this operation, it is so arranged that CCD IRCis selected.

Referring to FIG. 14, yet another embodiment of the present invention isshown. When compared with the first embodiment shown in FIGS. 8a and 8b,this embodiment has no photoelectric conversion elements IRD and VSD,and has only one CCD IRC, which is sensitive to infrared light.Furthermore, LED emits infrared light only when it is so determined thatthe data dF, calculated by the use of output from CCD IRC, is unreliabledue to low contrast.

An operation of the auto-focusing system of FIG. 14 is describedhereinbelow.

Referring also to FIG. 15 showing a flow chart of operation by thecircuit of FIG. 14, the steps up to step #10 is the same as those shownin FIG. 12a and, therefore, data dF is calculated using output signalfrom CCD IRC for the infrared light. Thus, the data dF is equal toamount and direction of defocus based on the infrared light. Then, atstep #51, it is discriminated whether or not a data of contrast asobtained through a calculation carried out in step #10 is above apredetermined level. If the contrast data is below a predeterminedlevel, the program advances to step #52 for producing a warning signalbecause the obtained data dF is unreliable. Then, at step #53, it isdiscriminated whether output 04 of microcomputer MCO is producing HIGH,or not. If output 04 is producing HIGH, it is understood that the datadF has been calculated with the aid of auxiliary infrared light.Therefore, in this case, there is no need to calculate the data dF againwith the aid of auxiliary infrared light, because there will be hardlyany difference in the newly calculated result. In this case, the programadvances to step #12.

Contrary, if output 04 is not producing HIGH, HIGH is produced fromoutput 04 and, thereafter, the program returns back to step #1 to repeatthe light measurement by the CCD IRC under the auxiliary infrared lightand the calculation of data dF.

While output 04 is producing HIGH to enable AND gate AN30 (FIG. 14), areset pulse produced from output .0.R is applied to set terminal offlip-flop FF20. Thus, flip-flop FF20 produces HIGH from its Q outputeffecting an emission of infrared light. Thereafter, when a transmissionpulse is produced from output .0.T, this pulse is applied through ANDgate AN31 and OR gate OR30 to reset terminal of flip-flop FF20. Thus,flip-flop FF20 produces LOW from its Q output stopping the emission ofinfrared light.

Next, at step #12, amount and direction of rotation of motor MO iscalculated using data dF, data S (or dL) and data K, as describedearlier. Then, after carrying out steps #14-#16, which are the same asthose shown in FIG. 12a, the program advances to step #55. A programincluding steps #55-#58 indicates the same operation of steps #17 and#18 shown in FIG. 12a, but in more details. At step #55, data Nrepresenting an amount of rotation of motor MO is stored in register M.At step #56, it is discriminated whether N is smaller than zero or not.If it is smaller than zero, motor MO is driven forward direction. If itis greater than zero, motor MO is driving backwardly. Thereafter, theprogram advances to step #19.

When the focus adjustment operation through steps #16, #35 and #37completes, the program advances to step #59 at which it is discriminatedwhether switch RS is turned on or not. If switch RS is not turned on, itis further discriminated whether switch MS is turned off by thediscrimination whether input i7 is receiving LOW. If input i7 is notreiving LOW, the above described operation is repeated, and when inputi7 receives LOW, display device DP is disabled, and LOW is produced fromeach of outputs 01 and 04, thereby returning microcomputer MCO to HALTcondition. Therefore, according to the flow chart shown in FIG. 15, whenone cycle of focus adjustment operation completes, it is necessary toopen the switch MS to start a new cycle of focus adjustment operation.

Furthermore, when it is discriminated that output i3 is producing HIGHas a result of closure of switch RS, output 04 produces LOW at step #63,and it is waited, after the completion of exposure control operation,until input i1 receives HIGH. When i1 receives HIGH, it is discriminatedwhether or not input i7 is receiving HIGH as a result of closure ofswitch MS. If input i7 is receiving HIGH, the program returns back tostep #1, thereby repeating the focus adjustment operation. If input i7is receiving LOW, the program advances to step #61 to end the operation.

It is to be noted that in FIG. 14, if switch RS closes to produce HIGHfrom AND gate AN0, a one-shot circuit OS20 produces a HIGH pulse whichis applied through OR gate OR30 to a reset terminal of flip-flop FF20.Accordingly, LOW is produced from Q output of flip-flop FF20 to stop theemission of infrared light.

Referring to FIG. 16, there is shown a flow chart which is amodification of the flow chart shown in FIG. 15. If it is discriminatedat step #51 that the image lacks contrast, and when it is discriminatedthat data dF is calculated with an aid of auxiliary light at step #53,it is understood that the situation in this case is such that the objectto be photographed is located very far from the camera. In this case,data Nm is set for the amount and direction of rotation of motor MO toshift the lens to the infinite focusing position. Thereafter, theprogram advances to step #14.

According to the modification of FIG. 14, only a CCD IRC, which issensitive to infrared light, is necessary for the optical arrangement offocus detection. From this view point, the circuit of FIG. 1a can besimplified such that photoelectric conversion device 9a may be deleted,or beam splitter 7 can be replaced with a filter which cuts lights otherthan infrared light, and the transmitted infrared light is relayedthrough a suitable relay lens to CCD IRC.

According to the modification described above in connection with FIG.14, infrared beam is emitted when an object has a low contrast, such aswhen aiming at a plain wall with a single color. In this case, thepurpose for emitting infrared beam is to present a contrast around thespot receiving infrared beam. To this end, the spot on which theinfrared beam impinges, or at least a border line of the lit spot shouldbe included in an area for the focus detection. Therefore, the diameterof the infrared beam for the above described modification should be madesmaller than that for the embodiments shown in FIGS. 8a and 8b and FIG.3.

Referring to FIG. 17, a detailed flow chart of step #51 shown in FIGS.15 and 16 for determining whether the contrast is low or not is shown.At step #80, a register C in microcomputer MCO is reset to "0", and atstep #81, a register i is stored with "1". Then, at step #82, anabsolute value of a difference between output ai from ith lightreceiving element and output ai+1 from (i+1)th light receiving element,which is substantially equal to the contrast difference between the twoneighboring light receiving elements, is added with the content ofregister C and the sum is stored in the same register C. Thus, registerC is now storing:

    |ai-ai+1|.

At step #83, "1" is added to the content of register i, and at step #84,the content of the register i is compared with a number n (n is equal tothe number of the total light receiving elements). If, the content ofregister i is smaller than n-1, the program returns back to step #82,thereby repeating the steps #82 and #82. Thus, the contrast differencesbetween the two neighboring light receiving elements are added for n-1times. When the content of the register i becomes equal to n-1, theprogram advances to step #85. At this step, the content of the registerC is storing:

    |a1-a2|+|a2-a3|+. . . +|an-2-an-1|+|an-1-an|,

which represents the contrast of the image.

At step #85, it is discriminated whether the content of the register Ccarrying a sum of the above formula is greater than a predeterminedvalue CD or not. If the content of the register C is greater than thevalue CD, this means that the image has an enough contrast. In thiscase, the program advances to step #12. Contrary, if the content of theregister C is not greater than the value CD, this means that thecontrast is relatively low and, therefore, the program goes to step #52.

Referring to FIG. 18, an example of an optical arrangement forinstalling infrared LED IRL is shown. Submirror 6 has two reflectionfaces 6a and 6b which are slightly slanted with each other. Light ray L1reflected from an object to be photographed and passing though thepicture taking lens reflects on reflection face 6a and impinges on beamsplitter 7. Infrared LED IRL is mounted on a base plate on which thebeam splitter 7 is provided. Infrared light ray L2 emitted from LED IRLreflects on reflection face 6b, passes through main mirror 1 and picturetaking lens, and directs to an object to be photographed.

It is to be noted that the light rays L1 and L2, when extended throughsubmirror 6, intersect with each other at a point 10a on film surface10. Accordingly, infrared LED IRL is installed as if light beam L2 isemitted from point 10a. Furthermore, emitted light beam L2 hits on aspot which is the same as the spot for the focus detection.

It is also to be noted that, from a practical point of view, reflectionfaces 6a and 6b may not be so precisely arranged as to intersect lightrays L1 and L2 exactly on the point 10a, but should be so arranged as iflight ray L2 emits not from the point 10a but from a point within a spotfor the focus detection.

Furthermore, according to the arrangement shown in FIG. 18, a plate 20is provided for holding beam splitter 7 and for intercepting infraredlight beam from LED IRL, thereby preventing the infrared light from LEDIRL from being directly impinged on the photoelectric conversion devices9a and 9b. Reference numerals 21, 22 and 23 designate a gear arrangementfor reducing the speed and transmitting the driving force of motor MO,and 24 is an actuator integrally provided to gear 23. When aninterchangeable lens is mounted on a camera, actuator 24 engages a shaft34 (FIG. 19). Thus, when actuator 24 rotates shaft 34, the focusingposition of the lens is changed, thereby carrying out the focusadjustment. Furthermore, 25 designates a rotating plate defining encoderEN, and 26 designates a separation plate for separating the camera intoa dark space and a lower space for intalling gears and motor MO.Separation plate 26 has an opening for the path of light beam from LEDIRL and light beam into the beam splitter.

Moreover, according to the arrangement shown in FIG. 18, relay lens 8aand 8b are both integrally formed by a transparent plastic and are heldby plate 20 together with beam splitter 7.

Referring to FIGS. 19 and 20, another example of an optical arrangementfor installing infrared LED IRL is shown. Instead of the camera body,LED IRL is provided in a filter F, which can be detachably mounted on aninterchangeable lens at its end remote from the camera-body receivingend. Filter F comprises a frame 30 having a threaded cylinder portionfor engagement with the lens and a pair of filter plates 31 and 32 whichare mold-formed by acrylic resin and each having a configuration of ahalfcircle. Filter plates 31 and 32 have, respectively, recessed face31a and projecting face 32a which are slanted 45° to the flat face ofthe filter plates. Filter plates 31 and 32 are accommodated in frame 30with faces 31a and 32a parallelly facing each other with a small air gaptherebetween. Filter plate 31 has a lens 31b formed thereon on oppositeside of recessed face 31a. Filter F also has an aperture plate 33 andinfrared LED IRL. The infrared beam emitted from the LED IRL passesthrough aperture plate 33, serving as F-stop, and lens 31b reflectstotally at face 31a, thereby emitting infrared beam from the center ofthe filter F and in alignment with the axis of the lens.

According to the arrangement shown in FIGS. 19 and 20, since there is noor very little angular difference between the projecting beam from thecamera to the object and reflected beam from the object to the camera,there will be no parallax observed between the projecting and receivingbeams. Furtermore, since the recess 31a, as well as the projection 32a,can be formed very small, it has little or no affect on the focusdetection or on the exposure operation.

Referring now to FIG. 21, an auto-focusing system according a furtherembodiment of the present invention is shown. The auto-focusing,according to the auto-focusing system of FIG. 21 is done by the contrastdetection, and this method is disclosed, e.g., in U.S. Pat. No.4,341,953 patented July 27, 1983 to Sakai et al, in Japanese PatentLaid-open Publication (Tokkaisho) No. 57-72110 or in Tokkaisho No.57-88418. A focus detection calculation circuit 13' shown in FIG. 21 isprovided to produce only the direction of defocus. When an image is blurbecause of front-focus, a terminal Ta produces HIGH, and when it is sobecause of rear-focus, a terminal Tc produces HIGH. And, when an imageis properly focused, a terminal Tb produces HIGH. Based on these HIGHsignals, a display DP' viewable through the viewfinder indicates afocused condition whether it is in front-focus, rear-focus or infocuscondition. Terminals Ta and Tc are also connected to AND gates AN40 andAN41, respectively, and terminal Tb is connected to an inverting inputof both AND gates AN40 and AN41. Motor drive circuit MDR is connected toan output of AND gate AN40 and also to an output of AND gate AN41through OR gate OR40. When AND gate 40 produces HIGH from its output,motor drive circuit MDR is so actuated as to drive the motor MO in,e.g., forward direction, thereby shifting the lens to infinite focusposition. Contrary, when OR gate OR40 produces HIGH from its output,motor drive circuit MDR is so actuated as to drive the motor MO in,e.g., reverse direction, thereby shifting the lens to near focusposition. Furthermore, when AND gate AN40 or OR gate OR40 stopsproducing HIGH to supply LOW from both AND gate AN40 and OR gate OR40,motor drive circuit MDR immediately stops the motor MO, thereby stoppingthe lens shift.

A one-shot circuit OS40 produces a HIGH pulse in response to HIGH fromterminal Tb, thereby setting flip-flop FF40. Thus, flip-flop FF40produces HIGH from its Q output. Furthermore, the HIGH pulse fromone-shot circuit OS40 is applied to counter CO40, thereby resetting thecounter CO40, which is provided for counting the number of pulses fromencoder EN, to zero. A digital comparator DC compared the tput ofcounter CO40 with data S (or dL) stored in a data reading circuit DR asobtained from data output circuit LDO provided in an interchangeablelens. When two signals match with each other, comparator DC produces LOWwhich is applied to AND gate AN42. An output of AND gate AN42 isconnected to OR gate OR 40. Furthermore, the output of comparator DC isconnected to one-shot OS41. Thus, in response to the change of outputfrom comparator DC from HIGH to LOW, one-shot circuit OS41 produces HIGHto reset flip-flop FF40.

The auto-focusing system according to the embodiment shown in FIG. 21operates as follows. When focus detection is started by infrared light,and when circuit 13' produces HIGH from its output terminal Ta, AND gateAN40 produces HIGH, thereby turning the motor MO forwardly to effect thelens shift toward infinite focus position. Then, when the lens isshifted to a position at which the image formed by infrared lightproperly focuses on a predetermined image forming plane, terminal Taproduces LOW and, at the same time, terminal Tb produces HIGH. Thus,one-shot circuit OS40 produces a HIGH pulse, thereby setting flip-flopFF40. Thus, flip-flop FF40 produces HIGH from its output Q. Thus, themotor MO is turned in the reverse direction to effect the lens shifttoward near-focus position. This lens shift is detected by encoder ENand counter CO40 and, when the lens shift is effected for a requiredamount determined by the data S (or dL) stored in data reading circuitDR, comparator DC produces LOW, thereby producing LOW from AND gate AN42and OR gate OR40. Since, at this moment, AND gate AN41 is producing LOW,motor drive circuit MDR receives LOW from OR gate OR40, therebyimmediately stopping the motor MO.

It is to be noted that when comparator DC changes its output, from HIGHto LOW, one-shot circuit OS41 produces HIGH, thereby resetting flip-flopFF40. Thus, flip-flop FF40 produces LOW from its Q output, therebydisabling AND gate AN42.

In contradistinction to the above, when focus detection is started byinfrared light, and when circuit 13' produces HIGH from its outputterminal Tc, both AND gate AN41 and OR gate OR40 produce HIGH, therebyturning the motor MO reversely to effect the lens shift toward nearfocus position. Then, when the lens is shifted to a position at whichthe image formed by infrared light properly focuses on the predeterminedimage forming plane, terminal Tc produces LOW and, at the same time,terminal Tb produces HIGH. Accordingly, AND gate AN41 produces LOW, butAND gate AN42 produces HIGH, because flip-flop FF40 produces HIGH fromits Q output due to the HIGH pulse produced from one-shot circuit OS40.Thus, OR gate OR40 continues to produce HIGH. Accordingly, motor drivecircuit MDR continues to drive the motor MO in the reverse direction.Thus, the lens shifts past the position for properly focusing an imageby infrared light. The amount of lens shift past said position isdetected by encoder EN and counter CO40 and, when the lens is shited fora required amount determined by the data S (or dL) stored in datareading circuit DR, comparator DC produces LOW, thereby immediatelystopping the lens in the same manner described above.

By the above described operation, the picture taking lens is shifted toa position at which the image formed by visible light focuses properlyon the predetermined image forming plane, thereby completing thecorrection of the deflection dL.

In contrast to the embodiments described.above in connection with FIGS.8a, 8b, 13 and 14 offering a one-step control system, the lens,according to the embodiment described above in connection with FIG. 21,is controlled in two steps. First, the lens is shifted to aquasi-infocus position basd on the focus detection carried out by theinfrared light. Secondly, by the use of a signal representing the data S(or dL) as obtained from data output circuit IDO provided in the mountedinterchangeable lens, the lens is further shifted to a true-infocusposition for the visible light. This two-step control system can beapplied to the previous embodiments of FIGS. 8a, 8b, 13 and 14, asdescribed below.

In the embodiments described above in connection with FIGS. 8a, 8b, 13and 14, focus detection is carried out by a so-called phase differencedetecting system. When the two-step control system is employed, the lensis first shifted to a quasi-infocus position based on the defocus signaldF as obtained from focus detection calculation circuit 13 and,thereafter, the lens is further shifted in accordance to the signal S(or dL) to the true-infocus position for the visible light. Morespecifically, the lens is first shifted until encoder EN producesN1=K.dF pulses. Thereafter, the lens is further shifted until encoder ENproduces N2=K.dL pulses. Accordingly, in total, the lens is shifted by adistance N=N1-N2=K(dF-S), which is substantially equal to the distanceof lens shift carried out in one-step control system.

In any one of the above described embodiments, various changes andmodifications can be adapted. For example, beam splitter 7 can beeliminated when the focus condition detection is carried out based ononly infrares light. In this case, an infrared light pass filter shouldbe provided between submirror 6 and photoelectric conversion device 9bfor transmitting only the infrared light to device 9b. When thisarrangement is employed, it is not necessary to take the optical lengthd/n for the infrared light between first and second reflecting faces 7aand 7b into consideration. Therefore, data output circuit 16 needs toproduce only the deflection signal dL.

Although the present invention has been fully described with referenceto several preferred embodiments, many modifications and variationsthereof will now be apparent to those skilled in the art, and the scopeof the present invention is therefore to be limited not by the detailsof the preferred embodiments described above, but only by the terms ofappended claims.

What is claimed is:
 1. In an auto-focusing system for use in a camerawhich includes:a camera body; an interchangeable lens detachably mountedon said camera body and having an objective lens; a predeterminedimage-forming plane for which said objective lens is to be adjusted tofocus visible light thereon; infrared light measuring means formeasuring infrared light having passed through said objective lens toform an infrared light image at said image-forming plane; focuscondition detecting means for detecting, based on the measurement bysaid infrared light measuring means, the focus condition of the infraredlight image on said image-forming plane, and for producing a focussignal indicating the detected focus condition; data producing means forproducing a deflection signal indicating a difference between animage-forming distance of said objective lens for infrared light andthat for visible light; calculation means for calculating, using saidfocus signal and deflection signal, the focus condition of a visiblelight image formed by said objective lens on said image-forming plane,and for producing a drive signal corresponding to the focus condition ofthe visual light image thus calculated; and drive means for driving saidobjective lens in accordance with said drive signal, thereby shiftingsaid objective lens to a position for properly focusing said visiblelight on said image-forming plane, said data producing means comprising:first transmitting means for transmitting digital signals from saidcamera body to said interchangeable lens; address data producing meansprovided in said interchangeable lens for producing address data inaccordance with said digital signals; a ROM provided in saidinterchangeable lens for storing, at a location specified by saidaddress data, deflection signal data intrinsic to said interchangeablelens; second transmitting means for transmitting said deflection signalfrom said interchangeable lens to said camera body; and storing meansprovided in said camera body for storing said deflection signal.
 2. Inan auto-focusing system for use in a camera having a camera body and aninterchangeable lens detachably mounted on said camera body, saidinterchangeable lens comprising:an objective lens; receiving means forreceiving digital signals fed from said camera body to saidinterchangeable lens; address data producing means for producing addressdata in accordance with said digital signals received by said receivingmeans; a ROM for storing, at a location specified by said address data,deflection data indicating a difference between an image-formingdistance of said objective lens for infrared light and that for visiblelight, said data being intrinsic to said interchangeable lens; andtransmitting means for transmitting said deflection data stored at saidlocation of said ROM from said interchangeable lens to said camera body.3. An interchangeable lens as claimed in claim 2, further comprisingfocal length data producing means for producing digital datarepresenting the set focal length of said objective lens, said ROMfurther storing different deflection data for different focal lengths atdifferent addresses, and said address data producing means producingcombined address data in accordance with said digital signals receivedby said receiving means and said focal length data produced by saidfocal length data producing means, whereby said ROM produces differentdeflection data for different focal lengths.
 4. An interchangeable lensas claimd in claim 2, further comprising focusing distance dataproducing means for producing digital focusing distance data between atarget object and said camera, said ROM further storing differentdeflection data for different focusing distances at different addresses,and said address data producing means producing combined address data inaccordance with said digital signals received by said receiving meansand said focusing distance data produced by said focusing distance dataproducing means, whereby said ROM produces different deflection data fordifferent focusing distances.
 5. An auto-focusing system comprising:anobjective lens; a predetermined image-forming plane for which saidobjective lens is to be adjusted to focus visible light thereon;infrared light measuring means for measuring infrared light havingpassed through said objective lens to form an infrared light image atsaid image-forming plane; focus condition detecting means for detecting,based on the measurement by said infrared light measuring means, theout-of-focus direction of the infrared light image on said image-formingplane, and for producing a focus signal indicating said direction; firstdrive means for driving said objective lens in a direction determined bysaid focus signal until said focus signal disappears, therebypositioning said objective lens to a position for properly focusing saidinfrared light on said image-forming plane; data producing means forproducing a deflection signal indicating a difference between animage-forming distance for infrared light and that for visible light;and second drive means for driving said objective lens based on saiddeflection signal, thereby shifting said objective lens to a positionproperly focusing said visible light on said image-forming plane.
 6. Inan auto-focusing system for use in a camera having a camera body and aninterchangeable lens detachably mounted on said camera body, saidinterchangeable lens comprising:an objective lens; receiving means forreceiving a signal fed from said camera body to said interchangeablelens; storing means for storing deflection data indicating a focusingerror due to aberration of said objective lens, said deflection databeing intrinsic to said interchangeable lens; and transmitting means fortransmitting the deflection data stored in said storing means to saidcamera body in accordance with said signal received by said receivingmeans.
 7. An interchangeable lens as claimed in claim 6, furthercomprising means for producing focal length data representing the setfocal length of said objective lens, said storing means further storingdifferent deflection data for different focal lengths, and saidtransmitting means transmitting the deflection data specified by saidfocal length data to said camera body in accordance with said signalreceived by said receiving means.
 8. An interchangeable lens as claimedin claim 6, further comprising means for producing focusing distancedata representing the set focusing distance, said storing means furtherstoring deflection data for different focusing distances, and saidtransmitting means transmitting the deflection data specified by saidfocusing distance data to said camera body in accordance with saidsignal received by said receiving means.
 9. A system for auto-focusingan interchangeable lens mounted to a camera body, wherein said camerabody comprises:focus condition detecting means for detecting a focuscondition of said interchangeable lens by light measurement through saidinterchangeable lens to generate a defocus digital signal representativeof the amount and direction of defocus of said image formed on apredetermined image-receiving plane with respect to a properly focusedimage thereon; drive means for effecting auto-focusing of saidinterchangeable lens; means for sequentially reading auto-focusingdigital data from said interchangeable lens, said auto-focusing digitaldata representative of a variety of auto-focusing factors of saidinterchangeable lens and intrinsic to said interchangeable lens;calculating means for calculating data representing the amount of driveto be effected by said drive means from said defocus digital data fromsaid focus condition detecting means and said auto-focusing digital datafrom said reading means; means for determining the direction of drive tobe effected by said drive means in accordance with the direction ofdefocus represented by said defocus digital data; means for producingdata corresponding to the amount of drive actually effected by saiddrive means; and means for stopping said drive means when data from saidcalculating means and data from said data producing means represents apredetermined relationship with respect to each other; and wherein saidinterchangeable lens comprises: an optical system adapted to be drivenby said drive means for a change-of-focus condition; a ROM storing saidauto-focusing digital data, said auto-focusing digital data stored insaid ROM including: (a) deflection data indicating a focusing error dueto optical aberration of said interchangeable lens, and (b) conversioncoefficient data for converting the amount of defocus represented bysaid defocus digital data into the amount of drive to be effected bysaid drive means for effecting auto-focusing of said interchangeablelens;means for sequentially designating addresses of said ROM forsequential output of said auto-focusing digital data including saidconversion coefficient data and said deflection data; and means fortransmitting said auto-focusing digital data sequentially output fromsaid ROM to said camera body for sequential reading of saidauto-focusing digital data by said reading means.
 10. A system asclaimed in claim 9, wherein said camera body further comprises means forproducing first and second digital signals, and wherein saidinterchangeable lens further comprises means for receiving said firstand second digital signals, said first signal received by said receivingmeans causing said address designating means to designate an address ofsaid ROM where said deflection is stored while said second digitalsignal received by said receiving means causing said address designatingmeans to designate an address of said ROM where said conversioncoefficient data is stored.
 11. A system as claimed in claim 10, whereinsaid interchangeable lens is a zoom lens and further comprises means forproducing digital data corresponding to a set focal length of said zoomlens, and wherein said ROM includes a set of addresses for storingvarious conversion coefficients corresponding to various zoom lens focallengths as said conversion coefficient data while said addressdesignating means is adapted to designate said set of addresses inaccordance with combinations of said second digital signal and saiddigital data from said digital data producing means.
 12. A system asclaimed in claim 10, wherein said interchangeable lens is a zoom lensand further comprises means for producing digital data corresponding toa set focal length of said zoom lens, and wherein said ROM includes aset of addresses for storing various deflection data corresponding tovarious zoom lens focal lengths while said address designating means isadapted to designate said set of addresses in accordance withcombinations of said first drgital signal and said digital data fromsaid digital data producing means.
 13. A system as claimed in claim 12,wherein said ROM further includes another set of addresses for storingvarious conersion coefficients corresponding to various zoom lens focallengths as said conversion coefficient data while said addressdesignating means is adapted to designate said another set of addressesin accordance with combinations of said second digital signal and saiddigital data from said digital data producing means.
 14. In a system forauto-focusing an interchangeable lens mounted to a camera body whichincludes focus condition detecting means for detecting the amount anddirection of a defocus of an image formed on a predeterminedimage-receiving plane with respect to a properly focused image thereonand drive means for effecting auto-focusing, said interchangeable lenscomprising:an optical system adaed to be driven by said drive means toeffect a change-of-focus condition; means for receiving digital signalsproduced serially from said camera body; a ROM storing various dataintrinsic to said interchangeable lens and including:(a) deflection dataindicating a focusing error due to an optical aberration of saidinterchangeable lens, and, (b) conversion coefficient data forconverting the amount of defocus detected by said focus conditiondetecting means into the amount of drive to be effected by said drivemeans for effecting auto-focusing of said interchangeable lens; meansfor sequentially designating addresses in said ROM in accordance withsaid digial signals for sequential output of said various data includingsaid conversion coefficient data; and means for sequentiallytransmitting said various data sequentially output from said ROM to saidcamera body.
 15. An interchangeble lens as claimed in claim 14, whereinsaid interchangeable lens is a zoom lens and further comprises means forproducing digital data corresponding to a set focal length of said zoomlens, and wherein said ROM includes a set of addresses for storingvarious conversion coefficient data corresponding to various zoom lensfocal lengths while said address designating means is adapted todesignate said set of addresses in accordance with combinations of apredetermined one of said digital signals from said receiving means andsaid digital data from said digital data producing means.
 16. Aninterchangeable lens as claimed in claim 14, wherein saidinterchangeable lens as a zoom lens and further comprises means forproducing digital data corresponding to a set focal length of said zoomlens, and wherein said ROM includes a set of addresses for storingvarious deflection data corresponding to various zoom lens focal lengthswhile said address designating means is adapted to designate said set ofaddresses in accordance with combinations of a predetermined one of saiddigital signals from said receiving means and said digital data fromsaid digital data producing means.
 17. An interchangeable lens asclaimed in claim 16, wherein said ROM includes another set of dressesfor storing various conversion coefficient data corresponding to variouszoom lens focal length while said address designating means is adaptedto designate said another set of addresses in accordance withcombinations of another predetermined one of said digital signals fromsaid receiving means and said digital data from said digital dataproducing means.
 18. In an auto-focusing system for use in a camerahaving an interchangeable lens and a camera body which is provided withfocus condition detecting means and drive means, said interchangeablelens detachably mountable to said camera body comprising:an objectivelens driven by said drive means for focusing; receiving means forreceiving first and second signals fed from said camera body to saidinterchangeable lens; storage means for storing deflection dataindicating a focusing error due ro aberration of said objective lens andconversion coefficient data for converting the amount of defocus of animage formed by said objective on a predetermined image-receiving planewith respect to a properly focused image thereon and detected by saidfocus condition detecting means into the amount of drive to be effectedby said drive means, said deflection data and said conversioncoefficient data being intrinsic to said interchangeable lens; and,transmitting means for transmitting said deflection data and conversioncoefficient data to said camera body in accordance with said first andsecond signals received by said receiving means, respectively.
 19. Aninterchangeable lens as claimed in claim 18, further comprising meansfor producing focal length data representing the set focal length ofsaid objective lens, said storage means further storing differentdeflection data and different conversion coefficient data for differentfocal lengths, said transmitting means transmitting the deflection dataand the conversion coefficient data specified by said focal distancedata to said camera body in accordance with said first and secondsignals, respectively.
 20. An auto-focusing system for use in a cameracomprising:an object lens; infrared light emitting means for emittinginfrared light toward a target object; focus condition detecting meansfor detecting the focus condition of an image of said target objectformed by said objective lens on a predetermined image-forming plane andfor producing a focus signal indicating the detected focuscondition;data producing means for producing a deflection signalindicating a difference between an image-forming distance of saidobjective lens for infrared light and that for visible light; means forselectively energizing said light emitting means; and, drive means fordriving said objective in accordance with both said focus signal andsaid deflection signal when the focus condition detection is effectedwith said light emitting means energized while driving said objective inaccordance with only said focus signal when the focus conditiondetection is effected with said light emitting means de-energized,whereby said objective lens is driven to a position for properlyfocusing said visible light on said image-forming plane, irrespectivelyof the energization and de-energization of said light emitting means.21. An auto-focusing system as claimed in claim 20, wherein saidenergizing means includes:brightness detecting means for detectingwhether or not said target object has brightness above a predeterminedlevel; and means for energizing said light emitting means only upondetection of the brightness below said predetermined level.